This invention relates to apparatus for use as a borescope of the orbital scanning type.
It is known to provide such borescopes in which a reflector is rotatably mounted to achieve lateral viewing in a direction which can be orbitally scanned. Typically the reflector is associated with a window at a distal end of a tube of the borescope suitable for insertion into inaccessible areas, the tube typically containing an optical relay which transfers an image reflected by the reflector to a viewing means within a housing to which the tube is connected.
Since the reflector provides a mirror image of the object being viewed it is customary to include an image inverter such as a dove prism to correct the image and typically such an inverter is included within the tube as part of the optical relay. A disadvantage of such an arrangement is that when positioning the inverter between the lenses of the optical relay the size of the inverter is limited to that of the diameter of the relay lenses. Its shape then restricts the amount of light that can be transmitted through the optical relay or in other words the effective aperture of the inverter is less than that of the optical relay. The brightness of the viewed image is thereby reduced.
A further problem is that the performance of the borescope is sensitive to any slight misalignment of the inverter thereby creating difficulties in achieving correct assembly during manufacture since readjustment may require dissassembly of the optical relay.
It is an object of the present invention to provide such apparatus with improved image brightness and to simplify its assembly.